1. Field of the Invention
The present invention relates to a turbocharger-based engine system, and more particularly, to a turbocharger-based engine system that optimizes a synergy effect of a plurality of separate devices for improving engine performance without detracting the layout of an engine room by combining the functions of the devices, and a method of improving fuel efficiency using the turbocharger-based engine system.
2. Description of Related Art
In general, vehicles are equipped with various devices for improving engine performance and fuel efficiency.
A turbocharger, which is a typical device, contributes to improving the performance and fuel efficiency of an engine by compressing the intake air supplied into the engine, using the exhaust gas.
However, it is difficult to appropriately keep up with a demand for saving fuel and improving fuel efficiency which has increased with the rise of issues, such as global high oil price, and improvement of fuel efficiency and environment-friendly technology under a variety of regulations, only with the turbocharger.
As an example for the issues, a supercharger, which is used with the turbocharger, may be considered. A belt-driven mechanical supercharger, a typical supercharger, is composed of a bypass control valve and a magnetic clutch.
When an engine system is composed of a turbocharger and a super charger, the bypass control valve is closed and the magnetic clutch is engaged such that the supercharger and the turbocharger are connected, and the turbocharger and the supercharger are simultaneously operated to suck air in series in a low-speed turbo-lag section, while the magnetic clutch is disengaged and the bypass control valve is opened such that air is sucked, not through the supercharger, in a normal driving condition.
In the engine system composed of the turbocharger and the supercharger, as described above, it is possible to improve the response speed and low torque of a spark-ignition engine equipped with a turbocharger by making the operation state of the supercharger different in accordance with the driving conditions.
As described above, however, the belt-driven mechanical supercharger, which is a typical supercharger, needs a valve and a clutch, such that the engine system is necessarily complicated.
On the other hand, another typical device that improves engine performance together with a turbocharger is an EGR (Exhaust Gas Recirculation), an exhaust gas recirculation system.
The EGR contributes to improving engine performance by operating the turbocharger with the exhaust gas discharged to the outside from the engine such that the intake air that is supplied into the engine is compressed and some of the exhaust gas is supplied back into the engine.
In general, the EGR falls into an HP-EGR (High Pressure EGR) that takes the exhaust gas (or called an EGR gas) before the turbocharger and an LP-EGR (Low Pressure EGR) that takes the exhaust gas behind the turbocharger.
The LP-EGR has the advantage of making it possible to use relatively clean exhaust gas with pollutants filtered through a TWC (Three Way Catalytic Converter) or a DPF (Diesel Particulate Filter), at low pressure/low temperature, unlike the HP-EGR, by sending some of the exhaust gas, which has passed through the TWC or the DPF after flowing out of an exhaust manifold through a turbocharger, to the front end of a compressor of the turbocharger such that the exhaust gas flow with the intake air into the intake manifold.
As described above, there are a turbocharger, a supercharger, and an EGR (particularly, LP-EGR) as devices that remarkably increase engine performance in an engine system and an engine system equipped with an appropriate combination of the devices (turbocharger+supercharger or turbocharger+LP-EGR) can be considerably increased in performance.
Therefore, it is possible to contribute to optimizing the engine system if it is possible to maximize the advantages of the device by using all of the turbocharger, supercharger, and LP-EGR in the engine system.
However, it is difficult to achieve optimum control that can increase the synergy effect of the devices when implementing the operation using the turbocharger, supercharger, and LP-EGR, which have individual operational features, and the configuration of the engine system equipped with the supercharger and the LP-EGR, which have complicate configurations, becomes necessarily complicated.
The complicate engine system significantly restricts the layout of an engine room, such that it is necessarily very difficult to simultaneously use a turbocharger, a supercharger, and an LP-EGR.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information faints the prior art already known to a person skilled in the art.